The antiacetylcholine activity of a series of substituted piperazine compounds was determined on the isolated guinea pig ileum preparation. It was found that the activity of the benzhydryl types was enhanced by quaternization with methyl, ethyl, or isopropyl salts. Halogen or methyl substitution on a benzene ring also increased activity. Some equalled the activity of atropine sulfate. Other types of structures produced less potency. Toxicities in mice, LD 50 values, were determined for the compounds.